Direct imaging and spectral identification of the interfaces in organic semiconductor-ferromagnet heterojunction

Abstract

Using x-ray spectromicroscopy, we studied the interface of pentacene (Pn)-cobalt (Co) heterojunction fabricated by thermal evaporation in an ultra-high vacuum environment. Through element-specific images and absorption spectroscopic analysis, we found evidences suggesting that part of the Co top layer penetrates into Pn film and hybridizes with molecules. As the Curie temperature of infiltrated Co clusters is dimension sensitive, the Co penetration would create an ill-defined interfacial region whose magnetization depends on the temperature and depth of cobalt penetration. The magnetic complexity at Pn/Co interface was found reduced after inserting a thin Cu layer between Pn and Co.